1. Field of the Invention
The present invention relates to a speed change gear mechanism for lathes to allow speed change without stopping the lathes.
2. Description of the Related Art
Lathes are widely used to process working pieces by cutting that depends largely from the speed of the chuck. Speed change is therefore very important to the quality of the resultant working piece. A central numerical control (CNC) lathe uses a serve motor to directly drive a chuck shaft to thereby perform variable-speed change without stopping. It is, however, found that the torque is reduced as the serve motor directly drives the chuck shaft. The horsepower of the motor must be increased if the user intends to increase the torque which results in a relatively high cost. Although pneumatic or hydraulic speed change devices and electronic clutches have been proposed, the cost is still relatively high. In addition, the lathe must be redesigned.
Conventional gearboxes are, therefore, used to perform cutting that requires high torque. This is because the main shaft may have a reliable high torque. Yet, the lathe must be stopped before speed change by means of manually operating a gear lever.
The present invention is intended to provide an improved speed change gear mechanism to solve the above problems.